1. Field of the Invention
This invention is directed to lubricant compositions consisting of oils of lubricating viscosity and greases prepared therefrom which provide excellent anti-rust or corrosion characteristics when certain novel additive materials are incorporated therein.
2. Description of the Prior Art
It is known to incorporate into lubricant compositions, for example greases and other lubricants of varying viscosities, various rust or corrosion-inhibiting materials to avoid the deleterious effect of humid or wet environmental conditions upon metal surfaces being lubricated. Among such materials are the alkali metal nitrites, e.g., sodium nitrite. In order to achieve an adequate degree of corrosion-inhibiting effect, the alkali metal nitrite had to be employed in an amount equal to at least 2 percent by weight of the total lubricating composition. However, even such low amounts resulted in the abrasion and deterioration of the metal surfaces coming in contact with such compositions. It was later discovered that this problem could be overcome by using relatively small amounts of alkali metal nitrites in conjunction with a N-carboxymethyl-alkenylsuccinic acid and in alkali metal phosphate (U.S. Pat. No. 3,278,427).
It is also known to use N-carboxymethyl-alkenylsuccinic acid in oils and fuels as an anti-rust agent. However, when it is used in greases in sufficient amounts to prevent rusting, it interferes with the grease thickener and forms a semi-fluid lubricant. In order to overcome this deleterious effect in greases, large quantities of sodium nitrite must be used, as well as a small quantity of N-carboxymethyl-alkenylsuccinic acid.
It has now been discovered that the use of alkali metal nitrites, especially sodium nitrite, can be totally eliminated from anti-rust or corrosion-inhibiting lubricating compositions without sacrificing corrosion-inhibiting effectiveness.